Electric induction impeder

ABSTRACT

An impeder for use in an electric induction welding process is provided. A cooling medium is circulated centrally through the impeder&#39;s magnetic material and between the interior of the impeder&#39;s high temperature enclosure and the exterior of the magnetic material within the impeder with the impeder entry and exit passages for the cooling medium located on the same side of the impeder.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of application Ser. No. 11/303,694,filed Dec. 16, 2005, now abandoned which application claims the benefitof U.S. Provisional Application No. 60/637,590, filed Dec. 20, 2004,both of which applications are hereby incorporated herein by referencein their entireties.

FIELD OF THE INVENTION

The present invention relates to impeders that can be used in electricinduction welding processes to form, for example, metal pipe or tubingfrom strip stock.

BACKGROUND OF THE INVENTION

Impeders are used in high frequency welded pipe and tube fabricationprocesses. They are one or more pieces of ferrite, or other magneticmaterial, that is placed inside a pipe or tube within the weld area.This magnetic material accomplishes two things. It increases theelectrical impedance of the inside current path of the tube, forcing thecurrent to flow on the vee edges of the tube instead. It is this currentthat heats the vee edges prior to forging them together in the weld box.Secondly, it creates a low magnetic reluctance path inside the tubebetween the apex of the weld vee and the rear of the tube. The lowerreluctance path becomes the preferred path for the magnetic field. Thusmore of the magnetic field generated by the tube welder's induction coilor contacts passes through the weld vee to utilize this preferred path,and the welding current induced on the vee edges is thereby increased.U.S. Pat. No. 4,443,677 further describes the induction welding processand one type of conventional impeders.

There are many practical problems encountered with conventionalimpeders. The magnetic field that the impeder carries causes losses inthe ferrite due to its finite resistivity and its coercivity. Theselosses heat the ferrite, and if heat is not removed through propercooling, the ferrite's Curie temperature (the temperature at which amaterial looses its magnetic properties) can be exceeded or the binderthat holds the ferrite material together can disintegrate. Ferrite is abrittle material and mechanical shock encountered during the tubefabrication processes can cause it to break into multiple pieces. Whenthis happens the effective magnetic properties are greatly reduced. Theferrite is usually enclosed in a jacket generally made from a fiberglasstype material. This helps protect the ferrite from mechanical shock andprovides a means for channeling cooling water to the ferrite. Whenfabricating smaller diameter tube, the diameter of the ferrite must beas large as possible so that the impeder does not magnetically saturate.This results in tight clearances between the ferrite and the casing.Thus the cooling water must not contain contaminants that can plug thecoolant passage between the ferrite and its casing. When this happens,the ferrite will fail almost immediately due to local over-heating.Temporary interruptions in the coolant supply can cause steam to developinside the impeder casing. When this happens, the ferrite cantemporarily exceed its Curie temperature and this can result in asection of “cold” or paste weld in the tube.

One object of the present invention is an impeder that does not requireinternal cooling. Another object of the present invention is to providean impeder with internal cooling that operates with improved efficiency.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention is apparatus for, and method of,electric induction welding with an impeder. The impeder is formed from ahigh temperature impeder element disposed in a high temperatureenclosure. The impeder element may be a plurality of solid wires formedfrom a magnetically conductive, high Curie temperature material, witheach of the wires electrically isolated from all other wires. The hightemperature enclosure may be formed from a suitable ceramic composition.Internal cooling may be via a closed or open cooling system where thecooling medium is circulated centrally through the impeder element andbetween the interior of the high temperature enclosure and the exteriorof the impeder element with entry and exit passages for the coolingmedium located on the same side of the impeder. In alternate examples ofthe invention the impeder element may be a ferrite, or a rolledmagnetically conductive sheet.

Other aspects of the invention are set forth in this specification andthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing brief summary, as well as the following detaileddescription of the invention, is better understood when read inconjunction with the appended drawings. For the purpose of illustratingthe invention, there is shown in the drawings exemplary forms of theinvention that are presently preferred; however, the invention is notlimited to the specific arrangements and instrumentalities disclosed inthe following appended drawings:

FIG. 1( a) is a longitudinal cross sectional view of one example of animpeder of the present invention that does not require internal cooling.

FIG. 1( b) is a cross sectional view of the impeder in FIG. 1( a) alongthe line A-A.

FIG. 2( a) is a longitudinal cross sectional view of one example of animpeder of the present invention with internal cooling.

FIG. 2( b) is a cross sectional view of the impeder in FIG. 2( a) alongthe line B-B.

FIG. 3( a) is a longitudinal cross sectional view of another example ofan impeder of the present invention with internal cooling.

FIG. 3( b) is a cross sectional view of the impeder in FIG. 3( a) alongthe line C-C.

FIG. 4( a) is a longitudinal cross sectional view of another example ofan impeder of the present invention with internal cooling.

FIG. 4( b) is a cross sectional view of the impeder in FIG. 4( a) alongthe line D-D.

FIG. 5 is a cross sectional simplified illustration of an arrangementfor an induction welding process wherein an impeder of the presentinvention is used.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like numerals indicate likeelements, there is shown in FIG. 1( a) and FIG. 1( b) a first example ofthe impeder 10 of the present invention. The impeder element 12comprises a bundle of high temperature solid wires 14 substantiallysurrounded by a high temperature enclosure 16. In this non-limitingexample of the invention the high temperature solid wires are formedfrom a suitable type of high Curie temperature magnetic material, suchas but not limited to, a class of iron-cobalt alloys known as permendurto form a cylindrical bundle. The term “high Curie temperature” as usedherein generally refers to a Curie temperature of approximately 235° C.or higher. Each wire is electrically isolated from each of the otherwires by means of a suitable insulation that may be formed by anoxidation process on the surface of each wire, or by any other suitablemethod. The term “high temperature enclosure” as used herein generallyrefers to an enclosure material capable of withstanding approximately200° C., or higher, depending upon a particular application, and may beformed from a suitable heat resistant material such as a ceramiccomposition. One non-limiting type of ceramic composition that may beused for the enclosure is a silicon-aluminum-oxynitride compositionknown as sialon. Alternatively a synthetic high temperature polymer,such as a polyaramid polyparaphenylene terephthalamide composition, forexample, in the form of a KEVLAR tape, may be used to form theenclosure. The enclosure may be cast around the plurality of wires usedin impeder 10. While the impeder in FIG. 1( a) and FIG. 1( b) has agenerally overall cylindrical shape, other shapes are suitable dependingupon a particular application. The term “wire” as used herein generallyrefers to a magnetically conductive material, which may be of any crosssectional shape, and have with a cross section, typically (but notlimited to) between 8 and 24 American Wire Gauge (AWG). Wires ofdifferent compositions may be used in other examples of the inventions,and the enclosure may be formed from multiple parts of different hightemperature material.

FIG. 2( a) and FIG. 2( b) illustrate a second example of the impeder 20of the present invention. In this example, the impeder element 22comprises a cylindrical ring of high temperature solid wires 24 that isenclosed in a high temperature enclosure 26. Non-limiting selection ofthe high temperature solid wires and enclosure is the same as thatdescribed above for the first example of the invention. Center passage28 is formed in the cylindrical ring of wires and provides a flow pathfor a cooling medium, such as but not limited to air, water or liquidnitrogen. Flow is from the INLET to the OUTLET as illustrated by thearrows in FIG. 2( a). A venturi element 21 can be optionally placed atthe inlet of the center passage to enhance the cooling effect of thecooling medium. While the impeder 20 in FIG. 2( a) and FIG. 2( b) has agenerally overall cylindrical shape, other shapes are suitable dependingupon a particular application. The ring of high temperature wires, forexample, may be of rectangular shape in cross section with a suitablepassage formed with the plurality of wires for the flow of a coolingmedium. More than one inlet or outlet ports may be provided dependingupon a particular application. In other examples of the invention morethan one passage may be provided through the impeder element.

FIG. 3( a) and FIG. 3( b) illustrate a third example of the impeder 30of the present invention wherein a closed loop cooling system is used.In this example, the impeder element 32 comprises a magnetic materialthat is enclosed within a high temperature enclosure 36. The magneticmaterial is in the shape of an open cylinder. The magnetic material maybe any suitable magnetic material such as a ferrite or the hightemperature wires described above, and the high temperature enclosuremay be a ceramic composition as described above. Center passage 38provides a flow path for a cooling medium through the impeder from theinlet, and can generally be referred to as a coolant entry passage. Morethan one coolant entry passages may be provided in other examples of theinvention. Annular region 39 forms a space between the inner wall of theenclosure and the magnetic material to provide a flow path around theimpeder to the outlet, and can generally be referred to as a coolantexit passage. Coolant flow through the impeder is as illustrated by thearrows in FIG. 3( a). In other examples of the invention the coolantexit passage may be provided with one or more passage walls thatselectively direct flow around the space between the inner wall of theenclosure and the magnetic material. More than one inlet or outlet portsmay be provided depending upon a particular application. As in thesecond example of the invention a venturi element can be optionallyplaced at the inlet to enhance cooling around the impeder.

FIG. 4( a) and FIG. 4( b) illustrate a fourth example of the impeder 40of the present invention which is similar to the third example aboveexcept that the cooling medium is provided in an open cooling systemwherein the cooling medium enters at the inlet and flows around impederelement 42 through annular passage 49 to exit out the outlet asindicated by the arrows in FIG. 4( a). Generally an open loop system isused when the cooling medium can also serve as the mill coolant, whichis used to wash away oils, oxides, slivers, and dirt generated duringmill processes. Alternatively the impeder element may be in the shape ofan open ring and the cooling medium will flow through the center passageof the ring. Impeder element 42 may be any suitable magnetic materialsuch as a ferrite or the high temperature wires described above, andhigh temperature enclosure 46 may be a ceramic composition as describedabove.

In all examples of the invention the impeder element may be a sheet ofhigh Curie temperature magnetic material, such as but not limited topermendur, that is rolled to form a generally cylindrical shape.Adjacent surfaces of the rolled material are electrically insulated fromeach other by any suitable method, including but not limited to anoxidation process. In examples of the invention wherein the impeder isinternally cooled with a cooling medium, the sheet can be rolled with abobbin or one or more removal spindles to form one or more coolantpassages within the impeder element. Suitable but not limiting thicknessof the sheet is in the range of the diameters stated above for the hightemperature wires used in other examples of the invention.

FIG. 5 illustrates one example of use of an impeder of the presentinvention in an electric induction welding process. Stock material 90,which may be a metal sheet, is driven through weld box 92 in thedirection indicated by the arrow to bring opposing edges of the stockmaterial together. AC current flowing through induction coil 94, whichsurrounds the stock material, creates a magnetic field that couples withthe stock material. Induced currents in the stock material weld theopposing edges of the stock material together as they pass through theweld box to form a product 96, such as a tube or pipe. An impeder of thepresent invention, for example impeder 10 shown in FIG. 1( a) and FIG.1( b), is inserted into the stock material generally in the region shownin FIG. 5.

In all examples of the invention wherein a cooling medium is used, acoolant with a high heat capacity, such as an oil-based coolant can beused to reduce the flow and pressure requirements for the coolingsystem. Using a return flow type impeder casing design such as thatillustrated in FIG. 3( a) and FIG. 3( b) with pumps at both the inletand outlet would allow the outlet pressure to be below atmospheric.Attaching a short hose through a one-way valve to the outlet side of theimpeder would allow the system to remove any excess mill coolant frominside the welded tube. Excess mill coolant inside the tube can causesteam blowback through the weld vee, if it is heated by a subsequentsteam annealing process. Additionally an advanced filtration system canbe used to remove all contaminants from the impeder coolant and therebyeliminate any cooling passage clogging problem. A refrigeration systemcan be used to remove the heat from the coolant and control its inlettemperature at just below the optimal temperature that maximizes themagnetic properties of the impeder. By applying a thermally designedtexture to the outside surface of the impeder, the laminar boundarylayer can be eliminated thereby greatly increasing the heat transferbetween the ferrite and the coolant. The term “thermally designedtexture” as used herein refers to any method of configuring the surfacewall or boundary of the magnetic material, when that wall or boundary isused as a boundary for the cooling medium passage, to reduce laminarboundary flow conditions from those existing when the wall or boundaryis substantially smooth, including application of a boundary walltexturing material over the magnetic material.

In all examples of the invention an optional inside cushioning liner canbe disposed between the high temperature enclosure and the impeder toreduce shock transfer to the impeder material, which can extend the lifeof the impeder. The inside of the casing or the liner can be molded withcooling passages and/or a special texture to create turbulence in thecoolant and thereby increasing the heat transfer between the ferrite andthe coolant.

If a ferrite is used as the impeder, the ferrite composition can beoptimized for high Curie temperature, and low coercivity and resistivelosses to integrate it with the cooling system and coolant employed.High temperature binder, possibly ceramic based, can be used to preventbinder disintegration.

It is noted that the foregoing examples have been provided merely forthe purpose of explanation and are in no way to be construed as limitingof the present invention. While the invention has been described withreference to various embodiments, it is understood that the words whichhave been used herein are words of description and illustration, ratherthan words of limitations. Further, although the invention has beendescribed herein with reference to particular means, materials andembodiments, the invention is not intended to be limited to theparticulars disclosed herein; rather, the invention extends to allfunctionally equivalent structures, methods and uses, such as are withinthe scope of the appended claims. Those skilled in the art, having thebenefit of the teachings of this specification, may effect numerousmodifications thereto and changes may be made without departing from thescope and spirit of the invention in its aspects.

1. An impeder for controlling the magnetic field path in a workpiece inan electric induction welding process, the impeder comprising: amagnetic material having at least one entry passage formed centrallytherethrough for an entry flow of a cooling medium at a first end of themagnetic material; and a high temperature enclosure surrounding themagnetic material, the exterior of the magnetic material spaced apartfrom the interior wall of the high temperature enclosure to form atleast one exit passage for exit flow of the cooling medium at the firstend of the magnetic material, the at least one exit passage incommunication with the at least one entry passage, the high temperatureenclosure having at least one inlet port connected to the at least oneentry passage for injecting the cooling medium into the at least oneentry passage and at least one outlet port connected to the at least oneexit passage for discharging the cooling medium from the at least oneexit passage.
 2. The impeder of claim 1 wherein the magnetic materialcomprises a ferrite material.
 3. The impeder of claim 1 wherein themagnetic material comprises a plurality of magnetically conductive, highCurie temperature solid wires assembled in a bundle, each of theplurality of wires electrically isolated from each other.
 4. The impederof claim 1 wherein the magnetic material comprises a rolled sheet ofmagnetically conductive, high Curie temperature material having adjacentsurfaces of the rolled sheet electrically isolated from each other. 5.The impeder of claim 1 further comprising a means for directing thecooling medium from the at least one outlet port to remove a millcoolant from the workpiece.
 6. The impeder of claim 1 further comprisinga thermally designed texture on the walls of the magnetic materialforming a boundary for the at least one entry and exit passages.
 7. Theimpeder of claim 1 further comprising a venturi element at the at leastone entry passage.
 8. The impeder of claim 1 further comprising an inletcooling medium pump at the at least one inlet passage and an outletcooling medium pump at the at least one exit passage to provide coolingmedium pressure below atmospheric pressure at the at least one exitpassage.
 9. An impeder for controlling the magnetic field path in aworkpiece in an electric induction welding process, the impedercomprising: a plurality of magnetically conductive, high Curietemperature solid wires assembled in a bundle, each of the plurality ofwires electrically isolated from each other, the plurality ofmagnetically conductive, high Curie temperature solid wires having atleast one entry passage formed centrally therethrough for an entry flowof a cooling medium at a first end of the plurality of magneticallyconductive, high Curie temperature solid wires; and a high temperatureenclosure surrounding the exterior of the plurality of magneticallyconductive, high Curie temperature solid wires, the plurality ofmagnetically conductive, high Curie temperature solid wires spaced apartfrom the interior wall of the high temperature enclosure to form atleast one exit passage for exit flow of the cooling medium at the firstend of the plurality of magnetically conductive, high Curie temperaturesolid wires, the at least one exit passage in communication with the atleast one entry passage, the high temperature enclosure having at leastone inlet port connected to the at least one entry passage for injectingthe cooling medium into the at least one entry passage and at least oneoutlet port connected to the at least one exit passage for dischargingthe cooling medium from the at least one exit passage.
 10. The impederof claim 9 further comprising a means for directing the cooling mediumfrom the at least one outlet port to remove a mill coolant from theworkpiece.
 11. The impeder of claim 9 further comprising a thermallydesigned texture on the walls of the magnetic material forming aboundary for the at least one entry and exit passages.
 12. An impederfor controlling the magnetic field path in a workpiece in an electricinduction welding process, the impeder comprising: a rolled sheet ofmagnetically conductive, high Curie temperature material having at leastone entry passage formed centrally therethrough for an entry flow of acooling medium at a first end of the rolled sheet of magneticallyconductive, high Curie temperature material; and a high temperatureenclosure surrounding the rolled sheet of magnetically conductive, highCurie temperature material, the exterior of the rolled sheet ofmagnetically conductive, high Curie temperature material spaced apartfrom the interior wall of the high temperature enclosure to form atleast one exit passage for exit flow of the cooling medium at the firstend of the rolled sheet of magnetically conductive, high Curietemperature material, the at least one exit passage in communicationwith the at least one entry passage, the high temperature enclosurehaving at least one inlet port connected to the at least one entrypassage for injecting the cooling medium into the at least one entrypassage and at least one outlet port connected to the at least one exitpassage for discharging the cooling medium from the at least one exitpassage.
 13. The impeder of claim 12 further comprising a means fordirecting the cooling medium from the at least one outlet port to removea mill coolant from the workpiece.
 14. The impeder of claim 12 furthercomprising a thermally designed texture on the walls of the magneticmaterial forming a boundary for the at least one entry and exitpassages.